Switch

ABSTRACT

A bistable push button overcenter switch having a pair of stable positions to which the movable contact is shifted by identical successive movement of the pushbutton. A tension spring is connected to the pivoted pushbutton and to a projection on the movable contact. Camming surfaces are associated with each of the fixed contacts to cam the free end of the movable contact toward the other stationary contact upon depressing the pushbutton to change the tilt of the movable contact and shift it laterally through an overcenter position.

United States Patent [56] References Cited UNITED STATES PATENTS 2,899,512 8/1959 Burch 200/67 D UX 2,950,366 8/ 1960 McRoberts et al. 200/68 3,317,688 5/ 1967 Cherry et a] 200/67 B UX 3,497,648 2/1970 Parkhurst 200/67 B UX Primary Examiner-David Smith, Jr. Att0rney-Prutzman, Hayes, Kalb & Chilton ABSTRACT: A bistable push button overcenter switch having a pair of stable positions to which the movable contact is shifted by identical successive movement of the pushbutton. A tension spring is connected to the pivoted pushbutton and to a projection on the movable contact. C'amming surfaces are associated with each of the fixed contacts to cam the free end of the movable contact toward the other stationary contact upon depressing the pushbutton to change: the tilt of the movable contact and shift it laterally through an overcenter position.

PATENTEU JAN 4mm SHEET 1 [1F 3 INVENTOR. PAUL T. FLUMM ATTORNEYS PATENTED JAN 4 I972 SHEET 2 BF 3 SWITCH This invention relates to electrical switches and is of particular significance to a snap action switch in which identical sequential movements of a single pushbutton are used to actuate the switch to either of its two stable positions.

It is an object of this invention to provide an improved switch mechanism for operating a bistable switch wherein successive identical operations of a single pushbutton operate the switch alternately to its two stable positions.

Another object of this invention is to provide a switch of the type described which is of simple design, is formed of a small number of parts, is reliable in operation and is easy to fabricate. Included in this object is the provision of such a switch having an improved operating mechanism suitable for a single pole, single throw switch or a single pole, double throw switch.

A further object of this invention is to provide an overcenter switch operating mechanism of the type described suitable for adaptation to meet miniature microswitch requirements.

With the foregoing and other objects in view, I have devised the preferred constructions illustrated in the accompanying drawing forming a part of this specification. It is, however,to be understood that the invention is not limited tothe specific details of construction and arrangement shown but may embody various changes and modifications within the scope of the invention.

In the drawings:

FIGS. 1A through 1E are a diagrammatic illustration of the underlying principles of this invention;

FIG. 2 is an exploded perspective view partly broken away illustrating a preferred form of my invention;

FIG. 2a is a perspective view of the fixed contract of the embodiment of FIG. 2;

FIG. 3 is a perspective view of the pushbutton operator of the embodiment of FIG. 2;

FIG. 4 and 5 are top views of modified forms of switches embodying my invention;

FIG. 6 is a top view of a movable contact element suitable for use in the switch of FIG. 4;

FIG. 7 is a side view of the movable switch element of FIG.

FIG. 8 is a fragmentary cross-sectional view along lines 8-8 of FIG. 4;

FIG. 9 is a cross-sectional view of a switch illustrating still another form of my invention taken along lines 9-9 of FIG. 10;

FIG. 10 is a cross-sectional view taken along the lines l0- 10 of FIG. 9;

FIG. 11 is a fragmentary cross-sectional view taken along the lines 11l1 of FIG. 9;

FIG. 12 is a fragmentary cross-sectional view taken along the lines l2l2 ofFIG. 9;

FIG. 13 is a fragmentary enlarged view of the contact, stop and camming means of the form of the invention shown in FIG. 10; and

FIG. 14 is a cross-sectional view taken along the lines 14- 14 ofFIG. 13.

Referring to the drawings in detail, FIGS. IA throughIE, inclusive, are diagrammatic illustrations of the underlying principles of a switch incorporating this invention.

FIG. 1A shows a movable contact element 1 having one end freely pivoted on a stationary terminal 3 at point 2 on the longitudinal axis A of the switch. A pushbutton operator 4, shown as being in its inoperative position, is provided with a pair of camming recesses 5 and 6 disposed symmetrically relative to a vertical plane through axis A. A pair of stops 7 and 8 disposed symmetrically relative to the vertical plane through axis A are provided with laterally extending flanges 7a and 8a to limit the upward movement of the free end 9 of movable switch element 1 underthe bias ofa tension spring 10, one end of which is connected to upstanding arm 11 of the movable switch element 1. The stops 7 and 8, one or both of which may be formed of electrically conductive material to provide stationary contact elements for the switch, are provided with camming disposed in laterally aligned face confronting relationship with respect to each other.

The upstanding arm 11 terminates at its upper end with a longitudinal projection 14 which engages the downwardly diverging sidewalls I5 and 16 of recesses 5 and 6. respectively. when the operator 4 is in its inoperative position.

As shown in FIG. IA, the end .17 of the spring 10 is fixed along the vertical plane through the longitudinal axis A of the switch above the pivot point 2 to bias the movable switch element I upwardly against flange 7a of stop 7. Moreover, the downwardly depending wall 15 of notch 5 of the operator 4 is disposed closer to the vertical plane through axis A than the wall 7!) of stop 7. Accordingly, the lateral movement of the projection 14 of the upstanding arm I] is more greatly limited than in the lateral movement of the free end 9 of movable switch element 1 so that when the upstanding arm II engages wall 15 of notch 5, the plane passing through point 2, end 9, and projection I4 (indicated by dashed lines in FIG. 1A) tilts to the right of end 17 of spring 10. As a result, the spring 10 also biases projection 14 against the wall 15 to hold the movable switch element in one of its two stable positions when the operator is released, or inoperative.

FIG. 18 illustrates the switch mechanism as the operator 4 is in a partially depressed position. As the operator 4 begins its downward movement, theprojection 14 of the switch arm 11 is cammed by the downwardly diverging wall 15 into the root of the recess 5. This slightly changes the title of the switch arm 11 of movable switch element 1. However, the plane defined by the pivot point 2, and the free end 9 and the projection 14 of the movable switch element 1 continuesto be tilted to the right ofthe end 17 of spring 10 as viewed in FIG. 1B.

Further downward movement of the operator 4 moves the free end 9 of the movable switch element 1 downwardly along wall 7b and into engagement with the camming surface 12 which shifts the free end 9 of the switch element 1 to the right as shown in FIG. 1C. The plane of the movable switch element 1 defined by the pivot point 2, and the projection 14 and the free end 9 of the movable switch element gradually shifts under the influence of camming surface 112 until it is coincident with the end I7 of biasing spring 10.

Further downward movement of the operator 4 shifts the end 9 into an overcenter position and the free end 9 of the movable switch element shifts to the right (FIG. 1D) into engagement with the camming surface 13 of stop 8 with a snap action under the bias of spring 10.

As the operator 4 is released, the end of movable switch element 1 moves upwardly along camming surface 13 until it engages wall 8b and flange 8a of the stop 8. Further upward movement of the operator 4 releases projection 14 of arm 11 from engagement with the root of recessS so that it may shift into the recess 6 of operator 4 under the bias of spring 10 and comes to rest against downwardly diverging arm 16 of notch 6 (FIG. IE) so that the movable switch element] is positioned in its second stable position.

During the next following downward movement of the operator 4, the camming surface 13 shifts the free end 9 of the movable switch element 1 to the left as viewed in FIG. IE until the plane defined by the points 2, 9 and 14 of movable switch element 1 are shifted to the other. side of end 17 of spring It), at which time the free end 9 of movable switch element 1 is snapped into engagement with the camming surface 12 of stop 7 by the biasing action of springlO. By spacing flanges 7a and 8a above camming surfaces 12, 13, respectively, by walls 7b, 8b, a preselected amount of downward movement of the movable switch element I is achieved before the movable switch element I starts to cam toward the opposite stop. Moreover, by forming the camming surfaces l2 and 13 of a conductive material and electrically connecting them respectively to their associated stops 7 and 8,. a wiping action occurs between the movable and fixed contact elements in making and breaking electrical contact, andthe contact areas where arcing may occur are isolated from the current carrying areas when the contacts are closed.

FIG. 2 illustrates a preferred embodiment of the invention formed of minimum parts and easy to fabricate. The switch of FIG. 2 is provided with a housing preferably molded from a suitable insulating material. As shown, one wall of the housing is provided with a pair of parallel slots 22, 24 which telescopically receive and mount a fixed contact 28 bottomed on the floor of housing 20. As shown, the contact 28 and its base plate 26 are formed from a single sheet of a suitable conductive material with base plate tabs 27 received in slot 22.

A contact assembly 30 is telescopically received in a second pair of recesses 32, 34 of the housing 20 and bottomed on the floor thereof. The contact assembly 30 is shown as being of a right angular configuration so as to abut against walls 36 and 38 to fix the contact assembly laterally and longitudinally of the housing. A freely pivotable movable contact element 42, shown as being formed of a wire having an upstanding intermediate looped portion 44, has one end pivotally mounted in a dimple 46 of the contact assembly 30. One end of the coiled tension spring 48 is secured to the upstanding looped portion to bias the movable switch element 42 upwardly against the ledge or stop 50 of the stationary contact 28.

A second fixed contact 55, which is a mirror image of contact 28, is provided with a base plate 52 similarly telescopically received in parallel slots 51, 53 formed in the opposite sidewall of the housing 20 so that contact 55 is in face confronting relationship with the stationary contact 28 with contact 28 and contact 55 arranged symmetrically relative to a vertical plane through the longitudinal axis of the housing and passing through pivot 46. It willbe understood that either contact 28 or contact 55 may be formed of an insulating material if it is desired to provide a single throw switch.

Terminal screws such as 54 may be provided for attaching electrical lines to the switch terminals.

In the embodiment of FIG. 2, a single pushbutton operator 58 is provided with a depending post 60 to which the end hood 62 of the spring 48 is attached. The end of the post 60 is received in an upwardly open recess 66 which is disposed in housing 20 along the longitudinal centerline of the switch. The end hook 62 straddles the sloping upper surfaces 67 of recess 66 to locate the end hook 62 above dimple 46 in a vertical plane through dimple 46 and the longitudinal axis of the housing. Alternatively, a notch 64 may be formed in the post 60 to retain the end hook 62 of the spring to the post.

As shown in FIGS. 2 and 3, the pushbutton 58 is provided with a pair of quadrant trunnion bearings 68, 70 which are journaled in complementary recesses 72, 74, respectively, of the housing to mount the pushbutton 58 for pivotal movement relative to the housing along the vertical plane of the housing through its longitudinal axis. The pushbutton 58, formed of an insulating material, is assembled with the ledge 84 of pushbutton 58 underlying the end 86 of an insulator plate 76. Plate 76 also overlies the top edge 78 of the housing in engagement with the upper surfaces of the baseplate 26, 30 and contact assembly 52. Lugs 80 of the housing are respectively received within the notches 82 of insulating plate 76. A cover plate 88 is positioned to overlie the insulating plate 76 with the pushbutton 58 disposed in the aperture 90 and the lugs 92, 94, 96, respectively, positioned in slots 98, 100 and 102 and bent downwardly to secure the switch in assembled construction.

As shown in FIG. 3, the pushbutton operator 58 has a pair of recesses 104, 106 symmetrically arranged laterally of the vertical plane of the housing for receiving the upper edge of the loop 44 of the movable contact element 42. Each of the recesses 104, 106 are provided with downwardly diverging walls 108 and 109, respectively, to limit the lateral movement of the loop 44 as previously described in connection with FIG. I.

The relative positioning of the ledge 84 of the pushbutton and the ledge 50 of the fixed contacts is such that when the pushbutton 58 is released, the loop 44 does not touch the root of either slot 104 or 106 to provide for pretravel of the pushbutton operator 58 relative to the movable switch element 42 thereby assuring positive electrical contact between the lower surface of the ledge 50 and the movable contact element 42 under the bias of spring 48.

The operation of the embodiment of the switch shown in FIG. 2 is the same as that of FIG. 1. The loop 44 of the movable switch contact 42 is disposed against wall 109 of recess 106 of pushbutton 58, and as the pushbutton is depressed. the camming surface 109 of contact 28 will, after a certain amount of pretravel, bottom the loop 44 in the root of recess 106 and move the free end of the movable contact element 42 laterally (toward the left as shown in FIG. 2) until the plane defined by the free end of the contact 42, the top of the loop 44 and the pivot point 46 passes overcenter with respect to the end 62 of the spring 48. At that time, the contact will move, by snap action, to the camming surface 112 of the stop 55. The ledge 84 of the pushbutton cooperates with ledge within the housing 20 to limit its downward movement after a short overtravel beyond the point of contact changeover. As the pushbutton moves upwardly, the free end of the contact 42 wipes along the camming surface 112 until its upward position is limited by contact with the ledge or stop 113 of contact element 55. The overtravel of the pushbutton 58 occasioned by its release permits the upper end of the loop 42 to move into the notch 104 of the pushbutton operator and come to rest against wall 108 thereof. A successive operation of pushbutton operator 58 shifts the movable contact element into engagement with contact 28 and positions the loop 44 in the notch 106.

According to another aspect of the present invention, the movable contact element may be provided with indicator means to denote the position of the switch with respect to the two stationary contact elements 26, 52. As shown in FIGS. 48, this may be accomplished by providing an extension on the free end of movable contact element 42 and, if desired, providing a covering 122 preferably formed of a colored luminescent material. In the single throw switch of FIG. 4, the extension 120 may be positioned in a plane offset from the plane of the contact element 42, as shown in solid line in FIG. 6, and the upper surface of the switch housing provided with a centrally disposed window so that the end 120 is visible when the movable contact element 42 engages the right stationary contact of the switch. The window may be provided with a lens to increase the brilliance and depth of the color of the covering 122.

For a double throw switch, the extension 120 is preferably positioned in the plane of movable contact element 42 (as shown in phantom in FIG. 6) and two lens filled windows provided (FIG. 5) so that the covering of extension 120 is visible in one window or the other for a positive visual indication of the location of the movable switch element at all times whether the movable switch element is in its right or left positron.

FIGS. 9 through 14 illustrate an embodiment of the switch design especially suitable for miniature microswitches. In this embodiment, a two part molded housing has a base pro vided with slots through the wall thereof for receiving formed stamped spade-type terminal elements 158, 160, 162, respectively. The terminal 158 is provided with a dimple 164 for receiving the pivot end of a stamped movable contact element 166. As shown in FIG. 9, a projection 163 on the interior wall of housing base 150 prevents the upward movement of terminal 162. Another projection 161 (FIG. 10) on the interior wall of housing cover 151 similarly-fixes the location of terminal 160. If desired, the edges of contacts 160, 162 which engage movable element 166 may be bent at right angles to the adjacent portions thereof to provide face rather than edge engagement with element 116. A rivet 153 secures the housing and its cover in assembled position.

The terminal 158 is provided with a bifurcated end 168 (FIG. 11) on which the downwardly bent end 170 of the operator element 172 is pivotally mounted with the end of spring 174 extending between the legs of the bifurcated end of terminal 158 and secured thereto below the pivot point. This design provides for the use of a higher proportion of spring strength to bias the movable and fixed contacts together than is normally found in microswitches.

The pivoted operator element 172 is provided with laterally extending wing portions 174, 176 providing a pair of laterally spaced recesses symmetrically disposed along the axis of the switch element 166. These recesses are engageable with the upstanding portion 180 of the movable switch element 166 and provide for pretravel of the operator element 172 relative to contact element 166. The insulated pushbutton 182 extends through an aperture in the housing and is received in a slideway 184. It is provided with lateral projections 186 to limit the upward movement thereof under the bias of spring 174. The operation of this embodiment of the design is identical to that hereinbefore described.

As shown in FIGS. 13 and 14, the contact terminals may be provided with a facing 190 of good contact material such as silver inlaid on a backing material formed of a less expensive conductor, such as copper or brass. Such facing may be placed on one or both faces of stationary contacts 160, 162 and on the mating sidewalls of movable contact element 166.

From the foregoing it is apparent that this invention provides a snap action switch of simple design which is capable of being formed of a small number of parts, is easy to fabricate and reliable in operation, and in which identical successive movements of a single pushbutton operator in the same direction actuates the switch sequentially to its two stable positions. It is further apparent that this invention provides a switch which is adapted for miniature microswitch requirements, for single throw or double throw operation, and wherein the condition of the switch may be visually indicated to the user.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

I claim:

1. A bistable overcenter switch operable to a pair of stable position by identical movements of an operator comprising an operator, a relatively movable switch element, a pair of stops for said movable switch element at least one of which comprises a contact element which cooperates with said movable switch element to make and break an electrical circuit, means biasing said movable switch element in a direction generally parallel to the path of movement of said operator, camming surfaces associated with said stops for camming said movable switch element laterally of the path of movement of said operator and means connecting said operator to said movable switch element in one direction of movement to shift the axis of said biasing means through an overcenter position relative to said movable switch element upon consecutive strokes thereof in said one direction to move the same alternately from one stop to the other.

2. The switch of claim 1 wherein each of said stops comprise a contact element.

3. The switch of claim 1 wherein said camming surfaces face each other so that each camming surface moves the movable switch element laterally toward the other stop.

4. The switch of claim 3 wherein said camming surface associated with each of said stops is formed of a conductive material electrically connected to its associated stop.

5. The switch of claim 4 wherein said pair of stops are symmetrically disposed on opposite sides of a plane defined by the path of movement of said operator.

6. The switch of claim 5 wherein said operator is provided with a pair of camming recesses engageable with a projecting portion of said movable switch element and the camming recess engageable with said projecting portion is alternated during successive actuations of the operator.

7. The switch of claim 6 wherein said biasing means shifts the point of contact of said projecting portion from one camming recess to the other when said movable switch element is in engagement with one of said stops.

8. The switch of claim 6 wherein the walls defining said recesses are symmetrically disposed on opposite sides of a plane defined by the path of movement of said operator and are spaced more closely to said plane than said stops for limiting the lateral movement of said movable switch element.

9. The switch of claim 1 wherein said biasing means com prises a spring which biases said movable switch element toward said operator.

10. The switch of claim 1 wherein said biasing means is a tension spring having one end connected to the operator to bias the operator towards its inoperative position and said movable switch element toward one of said stops.

11. The switch of claim 10 wherein the other end of said spring is connected to the portion of said movable switch element engageable with said camming recesses to shift said portion alternately from one camming recess to the other when the operator is returned to its inoperative position.

12. The switch ofclaim 11 wherein the said movable switch element is provided with a projecting arm to which said biasing means is attached to rotate said movable switch element upon each actuation thereof, said rotation being effective to shift said arm to indicate the condition of the switch.

13. The switch of claim 12 including a housing having a win' dow through which said arm is visible: to indicate the position of said movable switch element.

14. The switch of claim 13 in which said arm is offset relative to said movable switch element and is visible through said window only when the switch element: is in engagement with a predetermined one of said stops.

15. A bistable overcenter switch operable to a pair of stable positions by identical movements of an operator comprising a housing having a longitudinal axis, a movable switch element disposed within the housing and freely pivoted at a point on a plane passing through said axis, a spring having its relatively stationary end secured substantially in said plane at a point displaced from the pivot point and its other end connected to said movable switch element at a point spaced from said pivot point, stop means engageable with said movable switch element to limit the movement of the free end of said movable switch element laterally of and in the: direction of said plane under the bias of said spring, an operator operatively engagea ble with said movable switch element, and camming means engageable with said movable switch element for shifting said free end laterally relative to said plane upon an actuating stroke of said operator in one direction, said camming means engageable with said movable switch element for shifting said free end laterally in the opposite direction relatively to said plane upon the next identical actuating stroke of said operator in the same direction, said stop means including a relatively fixed contact cooperable with said free end of said movable switch element to make and break an electric circuit.

16. A switch as recited in claim 15 wherein said movable switch element has a portion offset from a line connecting said pivot point and said fixed contact and said other end of said spring is connected to said offset portion.

17. A switch as recited in claim 16 wherein said operator is provided with depending walls symmetrically disposed laterally of said plane and engageable with said offset portion of said movable switch element to limit the tilting of the offset portion relative to said plane.

18. A switch as recited in claim 17 wherein said stop means comprises two members symmetrically disposed laterally of said plane.

19. A switch as recited in claim 15 wherein said housing comprises a base portion and a cover portion and the walls of said base portion comprise slots extending to said cover portion for telescopically receiving said stop members.

20. A switch as recited in claim 19 wherein said cover portion is secured to said base portion and engages said stop means to fix their position in the housing.

21. A switch as recited in claim 15 in which said movable switch element is a sheet metal stamping having an offset portion and the spring is connected to said offset portion.

22. A switch as recited in claim 15 wherein a lateral extension is provided on said free end of said movable contact and said housing is provided with a window through which said lateral extension is visible to indicate the position of said free end relative to said stop means.

23. The switch of claim 22 wherein the extension is offset relative to the free end of the movable switch element and is visible only when the switch is in a particular one of its two stable operating positions.

24. The switch of claim 22 wherein said housing is provided with a pair of windows through which said lateral extension is selectively visible to indicate the position of said free end relative to said stop means.

25. The switch of claim wherein the spring is connected 

1. A bistable overcenter switch operable to a pair of stable position by identical movements of an operator comprising an operator, a relativeLy movable switch element, a pair of stops for said movable switch element at least one of which comprises a contact element which cooperates with said movable switch element to make and break an electrical circuit, means biasing said movable switch element in a direction generally parallel to the path of movement of said operator, camming surfaces associated with said stops for camming said movable switch element laterally of the path of movement of said operator and means connecting said operator to said movable switch element in one direction of movement to shift the axis of said biasing means through an overcenter position relative to said movable switch element upon consecutive strokes thereof in said one direction to move the same alternately from one stop to the other.
 2. The switch of claim 1 wherein each of said stops comprise a contact element.
 3. The switch of claim 1 wherein said camming surfaces face each other so that each camming surface moves the movable switch element laterally toward the other stop.
 4. The switch of claim 3 wherein said camming surface associated with each of said stops is formed of a conductive material electrically connected to its associated stop.
 5. The switch of claim 4 wherein said pair of stops are symmetrically disposed on opposite sides of a plane defined by the path of movement of said operator.
 6. The switch of claim 5 wherein said operator is provided with a pair of camming recesses engageable with a projecting portion of said movable switch element and the camming recess engageable with said projecting portion is alternated during successive actuations of the operator.
 7. The switch of claim 6 wherein said biasing means shifts the point of contact of said projecting portion from one camming recess to the other when said movable switch element is in engagement with one of said stops.
 8. The switch of claim 6 wherein the walls defining said recesses are symmetrically disposed on opposite sides of a plane defined by the path of movement of said operator and are spaced more closely to said plane than said stops for limiting the lateral movement of said movable switch element.
 9. The switch of claim 1 wherein said biasing means comprises a spring which biases said movable switch element toward said operator.
 10. The switch of claim 1 wherein said biasing means is a tension spring having one end connected to the operator to bias the operator toward its inoperative position and said movable switch element toward one of said stops.
 11. The switch of claim 10 wherein the other end of said spring is connected to the portion of said movable switch element engageable with said camming recesses to shift said portion alternately from one camming recess to the other when the operator is returned to its inoperative position.
 12. The switch of claim 11 wherein the said movable switch element is provided with a projecting arm to which said biasing means is attached to rotate said movable switch element upon each actuation thereof, said rotation being effective to shift said arm to indicate the condition of the switch.
 13. The switch of claim 12 including a housing having a window through which said arm is visible to indicate the position of said movable switch element.
 14. The switch of claim 13 in which said arm is offset relative to said movable switch element and is visible through said window only when the switch element is in engagement with a predetermined one of said stops.
 15. A bistable overcenter switch operable to a pair of stable positions by identical movements of an operator comprising a housing having a longitudinal axis, a movable switch element disposed within the housing and freely pivoted at a point on a plane passing through said axis, a spring having its relatively stationary end secured substantially in said plane at a point displaced from the pivot point and its other end connected to said movable switch element at a point spaced from said pivot point, stop means engageable with saId movable switch element to limit the movement of the free end of said movable switch element laterally of and in the direction of said plane under the bias of said spring, an operator operatively engageable with said movable switch element, and camming means engageable with said movable switch element for shifting said free end laterally relative to said plane upon an actuating stroke of said operator in one direction, said camming means engageable with said movable switch element for shifting said free end laterally in the opposite direction relatively to said plane upon the next identical actuating stroke of said operator in the same direction, said stop means including a relatively fixed contact cooperable with said free end of said movable switch element to make and break an electric circuit.
 16. A switch as recited in claim 15 wherein said movable switch element has a portion offset from a line connecting said pivot point and said fixed contact and said other end of said spring is connected to said offset portion.
 17. A switch as recited in claim 16 wherein said operator is provided with depending walls symmetrically disposed laterally of said plane and engageable with said offset portion of said movable switch element to limit the tilting of the offset portion relative to said plane.
 18. A switch as recited in claim 17 wherein said stop means comprises two members symmetrically disposed laterally of said plane.
 19. A switch as recited in claim 15 wherein said housing comprises a base portion and a cover portion and the walls of said base portion comprise slots extending to said cover portion for telescopically receiving said stop members.
 20. A switch as recited in claim 19 wherein said cover portion is secured to said base portion and engages said stop means to fix their position in the housing.
 21. A switch as recited in claim 15 in which said movable switch element is a sheet metal stamping having an offset portion and the spring is connected to said offset portion.
 22. A switch as recited in claim 15 wherein a lateral extension is provided on said free end of said movable contact and said housing is provided with a window through which said lateral extension is visible to indicate the position of said free end relative to said stop means.
 23. The switch of claim 22 wherein the extension is offset relative to the free end of the movable switch element and is visible only when the switch is in a particular one of its two stable operating positions.
 24. The switch of claim 22 wherein said housing is provided with a pair of windows through which said lateral extension is selectively visible to indicate the position of said free end relative to said stop means.
 25. The switch of claim 15 wherein the spring is connected to the operator to bias the same away from said movable switch element and said housing provides a stop to limit such movement of the operator.
 26. The switch of claim 25 wherein said stop for said operator is positioned so as to permit the operator to move upwardly a limited amount after the free end of the movable switch element engages said stop means.
 27. A switch as recited in claim 15 wherein said movable switch element has an offset looped portion and said other end of said spring is connected to said offset looped portion. 